Subsurface tanks containing volatile fluids must be periodically inspected for safety. As the tanks contain volatile fluid, care must be taken to prevent any electrical charges or even relatively small amounts of light from entering the tank while the volatile fluids are present. Consequently, to inspect subsurface storage tanks the tanks are generally first drained, cleaned and ventilated and then, visually inspection by inspection personnel.
Current methods of inspecting tanks such as those which enclose petroleum or other caustic chemicals, especially large tanks, are very expensive, generally costing more than $250,000 depending upon the size of the tank. Unfortunately, the tank is rendered unserviceable for a month or more as the tank is drained, ventilated and thereafter inspected. Worse yet, many subsurface tanks are inadequately tested due to the complexity and cost of testing, increasing the risk of severe safety concerns to the environment and personal in the area, as well as contamination of the tank contents.
U.S. Pat. No. 5,819,863, hereby fully incorporated by reference, describes a vehicle capable of operating in a volatile fluid. This vehicle uses wheels magnetically coupled to a metal tank. In an emergency, the wheels are magnetically decoupled from the tank, and a retrieval balloon, filled by an inert gas from a pressurized gas container within the vehicle, increases the buoyancy of the vehicle, and therefore propelling it upwards. The interior of the vehicle is pressurized with an inert gas to prevent an internal explosion. In the event of a leak, the inert gas will flow outward, into the volatile fluid and the vehicle will power off to prevent explosion. Unfortunately, once a leak occurs in the vehicle and the vehicle is powered down, it must be manually extracted. Generally, this will require the user to physically pull the vehicle up by its cabling. Furthermore, the exposure of the interior components of the vehicle to the volatile fluid, even if the vehicle is powered down, may be detrimental, posing safety risks or causing undesirable reactions such as corrosion of the interior components.
Unfortunately, the vehicle described in U.S. Pat. No. 5,819,863 may get stuck under various obstacles within the tank, whereby the vehicle must be abandoned or physically extracted by the operator, generally by dismantling the tank. Furthermore, the vehicle described in U.S. Pat. No. 5,819,863 uses magnetically coupled wheels, making the vehicle unusable in non-magnetic tanks. The magnetically coupled wheels limit the operator's perspective, which may be optimal when the vehicle is unattached from the tank wall.
Other attempts have been made to create a vehicle for tank inspection, however these vehicles generally do not have measures to prevent explosion creating severe safety risks when used in explosive environments if the tank is not completely emptied and vented before inspection.
Unfortunately, current devices and methods for the inspection of volatile tanks are cost prohibitive and time consuming, leading to sever safety risks. Although there has been some progress with in-situ, subsurface tank inspection vehicles, current devices and methods have been ineffective due to a lack of versatility and reliable extraction.